KVM: arm64: nv: Always evaluate HCR_EL2 using sanitising accessors

A lot of the NV code depends on HCR_EL2.{E2H,TGE}, and we assume
in places that at least HCR_EL2.E2H is invariant for a given guest.

However, we make a point in *not* using the sanitising accessor
that would enforce this, and are at the mercy of the guest doing
stupid things. Clearly, that's not good.

Rework the HCR_EL2 accessors to use __vcpu_sys_reg() instead,
guaranteeing that the RESx settings get applied, specially
when HCR_EL2.E2H is evaluated. This results in fewer accessors
overall.

Huge thanks to Joey who spent a long time tracking this bug down.

Reported-by: Joey Gouly <Joey.Gouly@arm.com>
Tested-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20250112165029.1181056-2-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_emulate.h

@@ -184,29 +184,30 @@ static inline bool vcpu_is_el2(const struct kvm_vcpu *vcpu)
 	return vcpu_is_el2_ctxt(&vcpu->arch.ctxt);
 }
 
-static inline bool __vcpu_el2_e2h_is_set(const struct kvm_cpu_context *ctxt)
+static inline bool vcpu_el2_e2h_is_set(const struct kvm_vcpu *vcpu)
 {
 	return (!cpus_have_final_cap(ARM64_HAS_HCR_NV1) ||
-		(ctxt_sys_reg(ctxt, HCR_EL2) & HCR_E2H));
+		(__vcpu_sys_reg(vcpu, HCR_EL2) & HCR_E2H));
 }
 
-static inline bool vcpu_el2_e2h_is_set(const struct kvm_vcpu *vcpu)
+static inline bool vcpu_el2_tge_is_set(const struct kvm_vcpu *vcpu)
 {
-	return __vcpu_el2_e2h_is_set(&vcpu->arch.ctxt);
+	return ctxt_sys_reg(&vcpu->arch.ctxt, HCR_EL2) & HCR_TGE;
 }
 
-static inline bool __vcpu_el2_tge_is_set(const struct kvm_cpu_context *ctxt)
+static inline bool is_hyp_ctxt(const struct kvm_vcpu *vcpu)
 {
-	return ctxt_sys_reg(ctxt, HCR_EL2) & HCR_TGE;
-}
+	bool e2h, tge;
+	u64 hcr;
 
-static inline bool vcpu_el2_tge_is_set(const struct kvm_vcpu *vcpu)
-{
-	return __vcpu_el2_tge_is_set(&vcpu->arch.ctxt);
-}
+	if (!vcpu_has_nv(vcpu))
+		return false;
+
+	hcr = __vcpu_sys_reg(vcpu, HCR_EL2);
+
+	e2h = (hcr & HCR_E2H);
+	tge = (hcr & HCR_TGE);
 
-static inline bool __is_hyp_ctxt(const struct kvm_cpu_context *ctxt)
-{
 	/*
 	 * We are in a hypervisor context if the vcpu mode is EL2 or
 	 * E2H and TGE bits are set. The latter means we are in the user space
@@ -215,14 +216,7 @@ static inline bool __is_hyp_ctxt(const struct kvm_cpu_context *ctxt)
 	 * Note that the HCR_EL2.{E2H,TGE}={0,1} isn't really handled in the
 	 * rest of the KVM code, and will result in a misbehaving guest.
 	 */
-	return vcpu_is_el2_ctxt(ctxt) ||
-		(__vcpu_el2_e2h_is_set(ctxt) && __vcpu_el2_tge_is_set(ctxt)) ||
-		__vcpu_el2_tge_is_set(ctxt);
-}
-
-static inline bool is_hyp_ctxt(const struct kvm_vcpu *vcpu)
-{
-	return vcpu_has_nv(vcpu) && __is_hyp_ctxt(&vcpu->arch.ctxt);
+	return vcpu_is_el2(vcpu) || (e2h && tge) || tge;
 }
 
 static inline bool vcpu_is_host_el0(const struct kvm_vcpu *vcpu)

arch/arm64/kvm/hyp/vhe/sysreg-sr.c

@@ -216,7 +216,7 @@ void __vcpu_load_switch_sysregs(struct kvm_vcpu *vcpu)
 	__sysreg32_restore_state(vcpu);
 	__sysreg_restore_user_state(guest_ctxt);
 
-	if (unlikely(__is_hyp_ctxt(guest_ctxt))) {
+	if (unlikely(is_hyp_ctxt(vcpu))) {
 		__sysreg_restore_vel2_state(vcpu);
 	} else {
 		if (vcpu_has_nv(vcpu)) {
@@ -260,7 +260,7 @@ void __vcpu_put_switch_sysregs(struct kvm_vcpu *vcpu)
 
 	host_ctxt = host_data_ptr(host_ctxt);
 
-	if (unlikely(__is_hyp_ctxt(guest_ctxt)))
+	if (unlikely(is_hyp_ctxt(vcpu)))
 		__sysreg_save_vel2_state(vcpu);
 	else
 		__sysreg_save_el1_state(guest_ctxt);